1. Field of the Invention
The present invention relates to a cooling unit for forcing a heat generating component like a semiconductor package to be cooled with liquid-like cooling medium and an electronic apparatus provided with the cooling unit, such as a portable computer.
2. Description of the Related Art
An electronic apparatus like a portable computer has a micro processing unit (MPU) for processing multi-media information such as characters, voices and animation. This MPU tends to increase generation of heat during its operation accompanied by currently increased processing speed and multiple functions. Thus, in order to ensure a stable operation of the MPU, it is necessary to intensify heat radiation performance of this MPU.
Conventionally, a portable computer loaded with a MPU generating a large amount of heat is equipped with an air-cooling type cooling unit for forcing the MPU to be cooled. This cooling unit has a heat sink thermally connected to the MPU and an electric fan for supplying cooling air to this heat sink.
In this cooling unit, heat from the MPU is transmitted to the heat sink and then discharged out of the computer through a flow of cooling air. Therefore, because according to the conventional cooling method, cooling air serves as a cooling medium for depriving the MPU of heat, the cooling performance of the MPU mostly depends on air feeding performance of the electric fan. If the feeding amount of cooling air is increased to aim at intensifying cooling performance of the MPU, the rotation amount of the electric fan is increased, so that there is produced such a problem that a large noise may be produced. Additionally, because in the portable computer, a housing for incorporating the MPU and electric fan is designed so thin in a compact body, it is difficult to secure a space for accommodating a large electric fan having an excellent air feeding performance and an ideal air feeding path inside the housing.
In near future, it is expected that the processing speed of the MPU for the portable computer will be further accelerated and the MPU will become multi-functional, and accompanied by this trend, the heat generation of the MPU increases tremendously. Thus, the conventional forced air-cooling system has a fear that the cooling capacity for the MPU becomes short or reaches its limit.
As a means for improving this, for example, Jpn. Pat. Appln. KOKAI Publication No. 7-142886 has disclosed so-called liquid cooling system employing liquid having a higher specific heat than air as heat transferring medium.
According to this new cooling system, a heat receiving header connected to the MPU thermally is disposed inside the housing and a heat radiating header is disposed inside the display housing supported by this housing. The heat receiving header and the heat radiating header are connected to each other through a circulating pipe in which liquid-like cooling medium flows.
Because according to this cooling system, cooling medium circulates between the heat receiving header and the heat radiating header, heat from the MPU is transmitted to the heat receiving header and after that, transferred to the heat radiating header via the cooling medium. Heat transferred to the heat radiating header is discharged to the atmosphere by diffusion by heat conduction to the display housing. For the reason, the heat radiating header is connected thermally to the display housing and the display housing is composed of metallic material having excellent heat conductivity.
Therefore, such liquid cooling system is capable of transferring heat of the MPU more effectively than the conventional forced air cooling system, thereby raising the cooling performance of the MPU.
Meanwhile, heat of the MPU transferred from the heat radiating header to the display housing is discharged to the atmosphere from the surface of the display housing through natural convection and heat radiation. Thus, as the amount of heat transferred to the display housing increases, the surface temperature of the display housing is raised. As a result, if user happens to touch the surface of the display housing when opening/closing the display housing or carrying the computer, he or she may feel discomfort or heat.
Further, according to the liquid cooling system, a heat radiating header inside the display housing is connected to a heat receiving header inside the housing through a circulating pipe. Thus, if a necessity of removing this display housing from the housing occurs to carry out maintenance on the interior of the display housing, the heat receiving header thermally connected to the MPU needs to be removed from the housing temporarily.
However, disassembly of the periphery of such a precision MPU not only leads to damage of the MPU but also may make inappropriate the positional relationship between the heat receiving header and the MPU upon installation of the heat receiving header. Thus, this is unfavorable in terms of maintaining reliability of thermal connection between the MPU and the heat receiving header.
If the MPU is loaded on a place difficult to access like a rear face of a circuit board, a troublesome work of disassembling the housing and taking out the circuit board is required. This work can be said to be inappropriate in viewpoint of operation efficiency and therefore, there is a room for improvement at this point.